This invention relates to impact-sensing systems for road vehicles. More particularly, it relates to an improved system for timing the initiation of deploying of devices such as airbags.
It is well known that the total available time for an airbag to effectively restrain occupants in a severe event is very short; accordingly, occupant restraining systems must have the ability to timely and reliably determine the occurrence of an impact and to deploy the airbags to an operative condition within the available time. On the other hand, the system must be immune to deployment during minor impact events for which airbag restraint is not needed.
There is also a need for an improved method for calibration of control systems for airbags and other such devices. It is common practice in calibrating such control systems to develop the required calibration data from measurements taken in actual impact testing of each new vehicle model (referred to as alpha-build prototypes) so that the control system calibration for that model is especially established according to its characteristics. The testing of a vehicle is time consuming and costly; accordingly, a calibration method is needed which does not require actual impact testing of vehicles.
In the prior art, attempts have been made to discriminate the severity of the impact event using acceleration and jerk signals which cannot be reliably generated from computer simulations, such as finite element analysis. Accordingly, it is highly desirable to have an algorithm which does not rely upon acceleration and jerk measures to discriminate the severity of an impact event.
There is a need for an impact-sensing algorithm which relies upon velocity-based measures which can be obtained without need for the alpha-build procedure of impact testing prototype vehicles to calibrate the sensing system. Preferably, the velocity-based measures are obtained by use of computer or finite element models (FEM) for calibration of sensing systems.
In the prior art, the Watanabe et al. U.S. Pat. No. 5,787,377 granted Jul. 28, 1998 describes an airbag ignition timing system which processes vehicle acceleration signals to predict when a passenger will reach a front surface of the airbag. The ignition timing circuit processes acceleration signals to obtain plural displacement signals and adds them together to derive a predicted displacement signal and compare it with a reference value. An ignition signal is issued in the event the predicted displacement signal exceeds the reference value. In this system, predicted occupant displacement and impact severity are processed in a parallel manner as distinguished from a sequential manner.
The Nitschke et al. U.S. Pat. No. 5,540,461 granted Jul. 30, 1996 discloses an occupant restraint system using velocity calculations based on a filtered acceleration signal. The occupant displacement and relative speed with respect to the passenger compartment are estimated and compared with presettable limit values.
The Adolph et al. U.S. Pat. No. 5,785,347 granted Jul. 28, 1998 discloses an airbag deployment system which includes a pre-impact sensor and an impact detection sensor to predict impacts and to determine the severity of the predicted impacts. Sensors disposed in the vehicle determine passenger location and activate the airbags accordingly. Single- or multi-stage airbags may be deployed in accordance with the impact severity.
In accordance with this invention, a vehicle impact-sensing system is provided which discriminates severe events which require actuation of safety devices from minor incidents which do not require such actuation. This is accomplished by use of one or more vehicle-mounted accelerometers and an associated signal processing algorithm in a microprocessor.
Further, the impact-sensing computer program is based on an algorithm which uses only velocity and displacement measures which can be reliably generated from computer simulations that discriminate the severity of an event. This is accomplished without the need for generating acceleration/jerk measures; thus, the algorithm enables math-based impact-sensing system calibration to reduce or eliminate the costly alpha-build vehicle tests.
Further, in accordance with this invention, predicted occupant movement, used as a measure to determine the firing time for deploying airbags, makes the actual sensing time close to the desired sensing time.
Further, in accordance with this invention, deployment of airbags is controlled by the steps of determining whether an impact event has a high likelihood potential and, if it does, calculating the predicted occupant movement using velocity-based measures. If the predicted occupant movement exceeds a predetermined movement threshold, impact severity measure is determined as a function of vehicle velocity change. If the impact severity measure exceeds a predetermined severity threshold, the airbag inflator is actuated.